The long-term goal of the proposed study is to understand the control of gene expression in photoreceptor cells. This proposal is designed to use the human cone transducin gene as a model for cone photoreceptor-specific gene expression. The components that are involved in the regulation mechanism are cis-acting elements and trans-acting factors. The cis- acting elements will be defined by transfecting retinoblastoma cells with an expression vector containing a reporter gene and a relevant DNA sequence. Trans-acting factors in the nuclei of retinoblastoma cells and in adult human retinas will be identified by DNase 1 footprinting and mobility shift assays. Protein-binding sites on cis-acting elements will be determined by methylation interference assays. The trans-acting factors identified will be cloned by screening a retina expression library with a specific cis-acting element. The identity of the trans- acting factors will be further confirmed by determining the partial amino acid sequences from the proteins or from the peptides. This work will generate new insights into gene expression in photoreceptors, and will provide a basis for the study of inherited retinal diseases at the molecular level.